Table 1 Summary of model inputs

Clinical data (Survival curves distribution)

 Weibull parameters for OS of T-DXd

Shape = 0.0031, Scale = 1.3497

[14]

Weibull

 Weibull parameters for OS of T-DM1

Shape = 0.0048, Scale = 1.35

[14]

Weibull

 Weibull parameters for PFS of T-DXd

Shape = 0.014, Scale = 1.1570

[14]

Weibull

 Weibull parameters for PFS of T-DM1

Shape = 0.1076, Scale = 0.8481

[14]

Weibull

 Weibull parameters for TTD of T-DXd

Shape = 0.0144, Scale = 1.2965

[14]

Weibull

 Weibull parameters for TTD of T-DM1

Shape = 0.0821, Scale = 1.0563

[14]

Weibull

Health state utilities

 PFS (SD)

0.7 (0.56–0.84)

[21, 22]

Beta

 PD (SD)

0.5 (0.4–0.6)

[21, 22]

Beta

Disutility due to AEs

 Surgery (SD)

-0.23 (0.179–0.26)

[23]

Beta

 Radiotherapy (SD)

-0.163 (0.134–0.18)

[24]

Beta

 Thrombocytopenia: 42.2 daya (SD)

-0.122 (0.098–0.146)

[18]

Beta

 Anemia: 42.9 days (SD)

-0.12 (0.096–0.144)

[18]

Beta

 Nausea: 36.2 days (SD)

-0.103 (0.082–0.124)

[18]

Beta

 Leukopenia: 42.2 days (SD)

-0.09 (0.072–0.1028)

[18]

Beta

 Neutropenia: 40.1 days (SD)

-0.09 (0.072–0.1028)

[18]

Beta

 Fatigue: 58.3 days (SD)

-0.29 (0.223–0.348)

[18]

Beta

 Aspartate aminotransferase increased 21 days (SD)

-0.157 (0.126–0.188)

[18]

Beta

 Interstitial lung disease (ILD): 51.1 days (SD)

-0.13 (0.099–0.15)

[18]

Beta

Grades 3–4 AEs incidence

 Grades 3–4 AEs incidence T-DM1 (%)

  Neutrophil count decreased

3.10%

[14, 25]

-

  Anemia

6.50%

[14, 25]

-

  White blood cell decreased

0.8%

[14, 25]

-

  Nausea

0.40%

[14, 25]

-

  Fatigue

0.80%

[14, 25]

-

  Increased AST

5.40%

[14, 25]

-

  Interstitial lung disease (ILD)

2.70%

[14, 25]

-

  Left ventricular ejection fraction (LVEF) decrease

0.40%

[14, 25]

-

  Thrombocytopenia

6.10%

[14, 25]

-

 Grades 3–4 AEs incidence T-DXd (%)

  Neutrophil count decreased

16%

[14, 25]

-

  Anemia

9.3%

[14, 25]

-

  White blood cell decreased

6.2%

[14, 25]

-

  Nausea

7%

[14, 25]

-

  Fatigue

5.8%

[14, 25]

-

  Increased AST

0.8%

[14, 25]

-

  Interstitial lung disease (ILD)

13.2%

[14, 25]

-

  Left ventricular ejection fraction (LVEF) decrease

0.4%

[14, 25]

-

  Thrombocytopenia

0.8%

[14, 25]

-

Patient characteristics

 Mean age

49.84 years

[15]

Normal

 Average weight (SD)

65 kg (12)

[15]

Normal

 Average body surface area (SD)

1.78 m² (0.3)

[15]

Normal

Costs ($)

 Unit price of T-DM1 (100 mg)

409 $

Local charge

-

 Unit price of T-DM1 (160 mg)

671 $

Local charge

-

 Unit price of T-DXd (100 mg)

1982 $

Local charge

-

 Unit price of Trastuzumab (150 mg)

88 $

Local charge

-

 Unit price of Trastuzumab (440 mg)

216 $

Local charge

-

 T-DM1 cost/cycle (21 days)

1152 $

-

-

 T-DXd cost/cycle (21 days)

6019 $

-

-

 Cost of PET scan (SD)

345 $ (35)

Local charge

Gamma

 Terminal care cost (SD)

3158 $ (345)

Estimated based on local data and expert opinion

Gamma

Model Structure

 Time Horizon

Lifetime

-

-

 Discount rate for cost and utility

5.8%

[26]

-